Clostridium difficile (“C. difficile” or “C. diff”) is an anaerobic, Gram-positive, spore-forming bacteria that can causes severe diarrhea and other intestinal disease. C. difficile spores are frequently found in hospitals, and although spores cannot cause infection directly, they can transform into the active infectious form when ingested. C. difficile infections include a wide range of clinical syndromes from simple diarrhea to pseudomembranous colitis associated with significant morbidity and mortality. Antibiotic-associated colitis is an infection of the colon caused by C. difficile that occurs when competing bacteria in the gut flora have been wiped out by antibiotics. It is the most common infection acquired by patients while they are in the hospital.
The majority of infections with C. difficile occur among persons aged 65 years or older and among patients in health-care facilities, such as hospitals and nursing homes. From 1996 to 2009, C. difficile rates for hospitalized persons aged 65 years or older increased 200%, with increases of 175% for those aged 65-74 years, 198% for those aged 75-84 years, and 201% for those aged 85 years or older. C. difficile rates among patients aged 85 years or older were notably higher than those for the other age groups (National Hospital Discharge Survey, Annual Files, 1996-2009).
Diagnosing C. difficile colitis commonly involves a test that detects toxins produced by C. difficile in a stool sample. There are two different C. difficile toxins that are capable of causing colitis, referred to as toxin A (tdcA) and toxin B (tcdB). Diagnostic tests for these toxins are available commercially. However, these tests are not perfect and can result in false positive tests (finding toxins when there is no C. difficile) and false negative tests (not finding toxins when C. difficile is present) can occur. For example, the possibility of a cross-reaction between C. difficile and C. sordellii is known. See, “Cloning and characterization of the cytotoxin L-encoding gene of Clostridium sordellii: homology with Clostridium difficile cytotoxin B”, Green et. al., Gene, 1995, 161:57-61). Thus, there is still a significant clinical need to develop molecular testing for detection of C. difficile that is more sensitive than culture and less susceptible to false positive or false negative results.